Question

191. Number of 1 Bits

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Description

Write a function that takes the binary representation of an unsigned integer and returns the number of '1' bits it has (also known as the Hamming weight).

Note:

• Note that in some languages, such as Java, there is no unsigned integer type. In this case, the input will be given as a signed integer type. It should not affect your implementation, as the integer's internal binary representation is the same, whether it is signed or unsigned.
• In Java, the compiler represents the signed integers using 2's complement notation. Therefore, in Example 3, the input represents the signed integer. -3.

 

Example 1:

Input: n = 00000000000000000000000000001011
Output: 3
Explanation: The input binary string 00000000000000000000000000001011 has a total of three '1' bits.

Example 2:

Input: n = 00000000000000000000000010000000
Output: 1
Explanation: The input binary string 00000000000000000000000010000000 has a total of one '1' bit.

Example 3:

Input: n = 11111111111111111111111111111101
Output: 31
Explanation: The input binary string 11111111111111111111111111111101 has a total of thirty one '1' bits.

 

Constraints:

• The input must be a binary string of length 32.

 

Follow up: If this function is called many times, how would you optimize it?

Solutions

Solution 1

class Solution:
  def hammingWeight(self, n: int) -> int:
    ans = 0
    while n:
      n &= n - 1
      ans += 1
    return ans

public class Solution {
  // you need to treat n as an unsigned value
  public int hammingWeight(int n) {
    int ans = 0;
    while (n != 0) {
      n &= n - 1;
      ++ans;
    }
    return ans;
  }
}

class Solution {
public:
  int hammingWeight(uint32_t n) {
    int ans = 0;
    while (n) {
      n &= n - 1;
      ++ans;
    }
    return ans;
  }
};

func hammingWeight(num uint32) int {
  ans := 0
  for num != 0 {
    num &= num - 1
    ans++
  }
  return ans
}

function hammingWeight(n: number): number {
  let ans: number = 0;
  while (n !== 0) {
    ans++;
    n &= n - 1;
  }
  return ans;
}

impl Solution {
  pub fn hammingWeight(n: u32) -> i32 {
    n.count_ones() as i32
  }
}

/**
 * @param {number} n - a positive integer
 * @return {number}
 */
var hammingWeight = function (n) {
  let ans = 0;
  while (n) {
    n &= n - 1;
    ++ans;
  }
  return ans;
};

int hammingWeight(uint32_t n) {
  int ans = 0;
  while (n) {
    n &= n - 1;
    ans++;
  }
  return ans;
}

Solution 2

class Solution:
  def hammingWeight(self, n: int) -> int:
    ans = 0
    while n:
      n -= n & -n
      ans += 1
    return ans

public class Solution {
  // you need to treat n as an unsigned value
  public int hammingWeight(int n) {
    int ans = 0;
    while (n != 0) {
      n -= (n & -n);
      ++ans;
    }
    return ans;
  }
}

class Solution {
public:
  int hammingWeight(uint32_t n) {
    int ans = 0;
    while (n) {
      n -= (n & -n);
      ++ans;
    }
    return ans;
  }
};

func hammingWeight(num uint32) int {
  ans := 0
  for num != 0 {
    num -= (num & -num)
    ans++
  }
  return ans
}

impl Solution {
  pub fn hammingWeight(mut n: u32) -> i32 {
    let mut res = 0;
    while n != 0 {
      n &= n - 1;
      res += 1;
    }
    res
  }
}